[FFmpeg-devel] [PATCH] Avoid running malloc/free for 0-sized allocs and return a pointer to const memory so we will still detect invalid writes to malloc(0) areas. This also fixes av_realloc to treat size == 0 specially.

[Reimar Döffinger]

---
 libavutil/mem.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/libavutil/mem.c b/libavutil/mem.c
index f0f18d1..134fcba 100644
--- a/libavutil/mem.c
+++ b/libavutil/mem.c
@@ -57,6 +57,8 @@ void  free(void *ptr);
 
 #endif /* MALLOC_PREFIX */
 
+static const int dummy_alloc;
+
 /* You can redefine av_malloc and av_free in your project to use your
    memory allocator. You do not need to suppress this file because the
    linker will do it automatically. */
@@ -72,7 +74,7 @@ void *av_malloc(size_t size)
     if(size > (INT_MAX-32) )
         return NULL;
     else if(!size)
-        size= 1;
+        return (void *)&dummy_alloc;
 
 #if CONFIG_MEMALIGN_HACK
     ptr = malloc(size+32);
@@ -125,6 +127,10 @@ void *av_realloc(void *ptr, size_t size)
     /* let's disallow possible ambiguous cases */
     if(size > (INT_MAX-16) )
         return NULL;
+    else if (!size) {
+        av_freep(ptr);
+        return (void *)&dummy_alloc;
+    }
 
 #if CONFIG_MEMALIGN_HACK
     //FIXME this isn't aligned correctly, though it probably isn't needed
@@ -138,6 +144,8 @@ void *av_realloc(void *ptr, size_t size)
 
 void av_free(void *ptr)
 {
+    if (ptr == &dummy_alloc)
+        return;
 #if CONFIG_MEMALIGN_HACK
     if (ptr)
         free((char*)ptr - ((char*)ptr)[-1]);
-- 
1.7.4.4